Free-space quantum communication with satellites opens a promising avenue for global secure quantum network and large-scale test of quantum foundations. Recently, numerous experimental efforts have been carried out towards this ambitious goal. However, one essential step - transmitting single photons from the satellite to the ground with high signal-to-noise ratio (SNR) at realistic environments - remains experimental challenging. Here, we report a direct experimental demonstration of the satellite-ground transmission of a quasi-single-photon source. In the experiment, single photons (~0.85 photon per pulse) are generated by reflecting weak laser pulses back to earth with a cube-corner retro-reflector on the satellite Champ, collected by a 600-mm diameter telescope at the ground station, and finally detected by single-photon counting modules (SPCMs) after 400-km free-space link transmission. With the help of high accuracy time synchronization, narrow receiver field-of-view (FOV) and high-repetition-rate pulses (76 MHz), a SNR of better than 16:1 is obtained, which is sufficient for a secure quantum key distribution. Our experimental results represent an important step towards satellite-ground quantum communication.
@article{arxiv.1306.0672,
title = {Experimental Single-Photon Transmission from Satellite to Earth},
author = {Juan Yin and Yuan Cao and Shu-Bin Liu and Ge-Sheng Pan and Jin-Hong Wang and Tao Yang and Zhong-Ping Zhang and Fu-Min Yang and Yu-Ao Chen and Cheng-Zhi Peng and Jian-Wei Pan},
journal= {arXiv preprint arXiv:1306.0672},
year = {2015}
}